Composite materials have been used extensively as structural materials in aerospace and other applications where high strength, lightweight materials capable of withstanding high temperatures are required. Recently, considerable efforts have been made to extend the thermal stability range of these materials, while retaining their good structural strength and without increasing the weight of these materials. Addition polymers such as epoxy resins may be used in conjunction with fillers or fibers to provide essentially void-free composite structures which exhibit good structural properties and are light in weight. These latter structures are, however, limited to temperature applications below about 150.degree.-175.degree. C. because of the thermal stability characteristics of epoxy resins.
In recent years, a number of polymeric materials having high temperature properties have been developed. Unfortunately, the early thermally stable systems in this class of materials were formed by condensation reactions with the evolution of by-products. In the fabrication of reinforced composite structures, the volatile by-products, which were evolved, formed voids in the structures, thereby weakening such structures.
Later developed polymeric systems included ethynyl end-capped oligomers and polymers which propagate and cure by addition reactions to form high molecular weight, thermally stable compositions. Such end-capping has been accomplished in a variety of ways. Bilow et al, U.S. Pat. No. 3,864,309, disclose polyimide oligomers having terminal acetylenic groups which are prepared by the reaction of aromatic dicarboxylic anhydride with 3-aminophenylacetylene. Evers, U.S. Pat. No. 4,147,858 discloses fluorocarbon ether bibenzoxazole oligomers having terminal acetylenic groups which are prepared by the reaction of certain perfluoroalkylene ether diimidate esters and certain perfluoroalkylene ether bis(o-aminophenols) followed by reaction with 2-amino-4-ethynyl-phenol.
Kovar et al, U.S. Pat. No. 3,975,444 disclose that ethynyl-substituted aromatic ortho-diamines are useful as end-capping agents for certain heterocyclic oligomers. Arnold et al, U.S. Pat. Nos. 4,098,825 and 4,108,926 disclose acetylenic end-capping using 3-ethynyl-p-toluene sulfonate.
More recently, the preferred end-capping agent appears to be a substituted terminal acetylene compound containing at least three carbon atoms and a hydroxy group on the carbon atom adjacent to the acetylene group. Arnold et al, U.S. Pat. No. 4,268,654 employ 2-methyl-3-butyn-2-ol as the end-capping agent.
All the above ethynyl-terminated compounds are useful as or in the preparation of thermosetting resins, particularly resins having improved thermo-oxidative stability.
Accordingly, it is an object of the present invention to provide novel thermally stable resins based on arylether compounds containing terminal phenylethynyl groups.
Other objects and advantages of the present invention will be apparent to those skilled in the art.